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Frank
You wrote, in commenting on R B Gordon's paper in the Journal of the Royal
Institute of Navigation (1964) 17. pp 125 - 147:
"The author describes
his attempts to measure INDEX ERROR using stars. He describes his miserable
results which he clearly cannot explain, and then from that experience he
asserts (without evidence; without data; much as you have done) that
star-star sights for arc error wouldn't work. He has ZERO data on the topic
of using star-star distances for arc error."
What you say about his lack of data is fair enough, but isn't estimating index
error by using a star the simplest case of a star-star sight? If one accepts
this, may we then accept that sights using two stars are likely to have
similar errors? In my case, using a SNO-T sextant with x6 telescope clamped
atop a theodolite tripod the standard deviation of index error observations
using a star was 0.17 minutes (n = 30).
I am not a fan of Galilean 'scopes and Gordon seems to have been particularly
unlucky with his if he found "...a star image will superimpose over a range
of 5'."
Bill Morris
Pukenui
New Zealand
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